A Chinese intelligence ship has been shadowing the Alaskan coast for several days, likely because of America's missile defense system test, according to a CNN report.

The network quotes Navy Capt. Scott Miller of the the North American Aerospace Defense Command as saying the Chinese vessel is either a "communications" or "intelligence" ship.

U.S. officials said it's been roughly 100 miles off the coast of Alaska in international waters, arriving there before this week's Terminal High Altitude Area Defense (THAAD) missile defense test, which saw a missile launched from Kodiak, Alaska intercept another missile dropped from a military plane over the Pacific Ocean.

The missile defense system will soon be deployed to South Korea and is designed to shoot down a North Korean missile if the rogue nation attacks the U.S. or one of its allies. China, however, claimed the system could be used to intercept one of its own missiles.

One U.S. official told CNN it's likely the Chinese spy ship was near Alaska to keep tabs on the missile defense test.

Other Chinese ships have been spotted off the coast of Guam and near a joint U.S.-Australia military exercise, CNN reports.

U.S. and China relations have been frayed in recent years, partially over North Korea. China has friendly relations with the reclusive country and trades with it, a point of contention with the U.S.

President Donald Trump tweeted last week about the increase in trading between China and North Korea:

Trade between China and North Korea grew almost 40% in the first quarter. So much for China working with us - but we had to give it a try!